1. Field of the Invention
This invention relates to traffic controllers, and more particularly to a traffic phase sequencer within a traffic controller.
2. Description of the Prior Art
Heretofore the phase sequence and interval timing in traffic controllers has been accomplished by a slowly revolving cammer and cam operated switches in series with solonoids which energized the traffic lights. The sequence and interval lengths could be changed only by disassembling the camming mechanism and reordering and repositioning the cams. Reprogramming a traffic intersection could involve replacing the cam from a cam inventory.
It is therefore an object of this invention to provide a traffic controller that may easily be reprogrammed and does not require an inventory of special parts.
Advancing the yellow cam in this prior art traffic controller to lengthen the yellow interval resulted in shortening the preceding green interval. The continuously rotating cammer defined a fixed complete cycle time and a rigid time relationship among the intervals forming the complete cycle. Similarly, if an entire green-yellow-red phase were skipped for lack of DEMAND the timing of the other phases was disrupted.
It is therefore another object of this invention to provide a traffic controller in which each colored interval may be adjusted in period without affecting the adjacent intervals, and in which an entire phase may have a DEMAND contingency status without affecting the other phases.
Further, if one of the cam operated switches of this prior art device malfunctioned, synchronism between the cams and the colored traffic lights was lost causing the time intervals to be applied to the wrong light color. Homing cams periodically restored synchronism, but in the meantime the color intervals had unusual time periods which confused motorists.
It is therefore a further object of this invention to provide a traffic controller which has inherent and absolute synchronization between the interval time period and the interval color.
The prior art cams frictionally engaged cam followers and mechanically displaced them to operate the switches. The displaced cam followers were returned to the uncammed position by return springs. Overcoming this spring load and the friction introduced thereby required a finite force which dictated a suitably powered camming motor, and a heavy frame member capable of withstanding the strains thus generated. Further, misalignment of the axis of rotation due to wear or low manufacturing tolerences increased the frictional engagement between adjacent moving surfaces which increased the motor load.
It is therefore yet another object of this invention to provide a traffic controller sequencer which does not frictionally engage or displace cooperating structure and therefore has a lower power and weight requirement.